1. Field of the Invention
The present invention relates to an apparatus and method for measuring the individual toe angle of nonsteerable rear wheels on a vehicle, and more particularly to such apparatus and method for measuring individual toe angles of the rear wheels relative to a chassis centerline reference.
2. Description of the Prior Art
An electronic wheel aligner for measuring the toe of the front wheels with respect to the rear wheel axis of rotation is disclosed in U.S. Pat. No. 4,097,157, Lill. When the aligner heads are mounted on the rear wheels the system disclosed in the aforementioned U.S. Patent cannot determine the individual rear wheel toe because the reflector disclosed therein which provides the rear wheel rotation axis reference would then be mounted on a steerable front wheel having a movable rotation axis.
"Centering gages" for vehicle frames have been described in the past as for example in U.S. Pat. No. 3,151,396, Junkins. The gage disclosed by Junkins has a housing with a pair of elongate parallel bars which are simultaneously movable longitudinally in opposite directions within the housing. The outer end of each bar has a hanger attached thereto so that the end of each bar may be hung from opposite side beams on the vehicle frame. A rod is mounted on the housing which is always at the midpoint between the ends of the movable parallel bars since the ends of the bars either converge or diverage at the same rate due to an array of cables and rollers mounted within the housing.
Another "centering gage" is disclosed in U.S. Pat. No. 3,417,479, Hirmann, which includes members near the outer ends of the assembly which contact the vehicle chassis at similar points on opposite sides of the chassis. Telescoping end members are provided to move longitudinally on each end of a tubular center member in the Hirmann gage. A rack is attached to each of the telescoping end members extending into the center member. A pinion is mounted within the center member which is meshed with each of the two racks. Thus, when one telescoping end member is moved longitudinally either toward or away from the center of the gage, the pinion is rotated thereby driving the other telescoping end member toward or away from the center of the gage synchronously with the one telescoping end member. An optical path is aligned with the center point of the central member so that a line of sight is provided along the chassis centerline when the feeler members are in contact with opposite sides of the chassis.